This invention relates generally to optical transparencies and, more particularly, to optical transparencies that incorporate antireflection or antiglare coatings on substrates.
Optical transparencies of this particular kind have been developed to provide reduced reflectance and glare and thereby to enhance the readability of information displayed on or through them. It is known that antireflection coatings of low refractive index, as well as antireflection coatings of porous materials, can reduce the specular reflectance of the underlying substrates. However, such coatings can be readily applied only to limited kinds of substrates, and they frequently exhibit relatively poor mechanical properties.
Many commercial antireflection and antiglare coatings also have the disadvantage of sharply limiting the intensity and clarity of transmitted light. Some of these coatings are even highly translucent. In addition, because some of these coatings have significant surface roughness, they often are accompanied by visible defects.
Some antireflection coatings include multiple layers of alternating high refractive index and low refractive index materials. Although these coatings generally exhibit low reflectivity without sacrificing high transmittance and clarity, they can be relatively expensive to produce. In addition, even though such coatings provide relatively low specular reflectance, surface defects frequently are considered to be unduly visible. This has detracted from the suitability of the coated substrates for use as display cover panels.
It should, therefore, be apparent that there is a need for an improved antireflection coating for a transparent substrate, and a method for making it, which provides high transmittance with low specular reflectance, yet which also provides sufficient diffuse reflectance to result in low visibility of surface defects. The antireflection coating also needs to be chemically, mechanically and environmentally stable. The present invention fulfills this need.